The present invention relates to flat processing systems and, more particularly, drop stackers for collecting envelopes processed by a envelope mail system.
Conventional drop stackers are intended to collect envelopes processed by a mail processing system and delivered to the drop stacker in a seriatim manner. In a novel mail processing system, the processing system includes a feeder section having a non-contact moistener and a mailing machine which receives envelopes from the feeder section. The feeder section includes several modules. The first module is a hopper which receives a stack of mixed sized mail, sealed and unsealed, and flapped and unflapped. A singulator module separates the stacked envelopes and seriatimly delivers the envelopes to a moistener feeder section. It is the function of the moistener section to moisten the flap area of unsealed envelopes. After flap moistening, the envelope is passed to a mailing machine where the envelope is optionally weighed and printed with a postage indicia. After posting of the envelope, the envelope is ejected into a stacker for collection. One such stacker is referred to as a drop stacker.
It has been empirically observed that when employing a conventional drop stacker with the novel mail processing system, the ejection of the envelope stream into the drop stacker has exhibited a shingling problem in which the flaps of adjacent envelopes becoming glued together. This is the result of the flaps being able to open during their flight path and being able to get between the previously stacked envelopes and the rear wall. The ability of the envelope flaps to open is seen to be largely a consequence of the high processing speed of the mail processing system. The envelope sealing glue does not have sufficient time and contact with the opposite surface to become sufficiently tacky to hold the envelope flap closed by the time that the envelope is delivered to a stacker. Consequently, the stacker has to accomplish four functions. One is to assure that the hinge line of each envelope added to the stack is registered against the registration wall to minimize the opportunity for a following envelope flap to slip between the stack and the registration wall. A second is to provide for limiting the maximum angle the flap has a chance to open to less than 90 degrees. A third is to be able to close the flat against the resistant spring forces trying to open the flap. Lastly, the force must be provided to hold the flap closed and in contact with the mating portion of the envelope while sufficient adhesion is developed.